Many modern network-connectable, electronic devices require data connectivity as well as connection to power supplies. IP telephones, wireless LAN access points, Bluetooth access points, web cameras, digital still and video cameras, computers, tablets, liquid crystal displays, point-of-sale kiosks, network intercom systems, cellular telephones, security systems, gaming systems, etc. are examples of devices that require both data connectivity as well as connection to power supplies. Traditionally, each of these electronic devices had separate cables for data connectivity and power supply. With the advent of implementation of IEEE 802.3.af and IEEE 802.3.at standards, which are extensions of the existing Ethernet standard, power over Ethernet capability (i.e., supplying power over Ethernet cables) has become more common.
There are many advantages to supplying power over Ethernet. For example, power over Ethernet may result in more flexible network design because the powered devices can be situated in areas without access to power outlets. This may also result in cost savings because it removes the need to install additional power outlets. In addition, power over Ethernet may be safer because there is no need to deploy AC main power throughout the network. Thus, additional electronic devices will be designed to receive power over Ethernet for the reasons above, as well as because of higher power supply capabilities permitted under the standards. This is especially the case because the cost of adding power supplies to Ethernet switches is relatively low.
According to the existing standards, power sourcing equipment (PSE) executes a discovery process to determine whether a compatible device is connected to it before supplying power in order to prevent damage to the connected device. The PSE makes this determination by applying a relatively low voltage to the network cable and checking for the presence of a sensing resistor in the connected device. The PSE only supplies the full voltage after detecting the sensing resistor in the connected device. However, if the connected device includes a chargeable power storage device, the PSE continues to supply the full voltage so long as the PSE senses the sensing resistor, even after the power storage device attains full charge. This results in unnecessary power consumption.